US7963337B2 - Composite enhanced metallic drilling riser system - Google Patents

Abstract

An offshore composite enhanced metallic drilling riser is equipped to enable preloading of the composite shell and the metallic riser. A riser has steel end connectors and a continuous metallic inner liner, encased in a composite shell. A segmented hyperboloid shaped profile is located near each of the end fittings for preloading of the composite and the metallic riser. In one version, both halves of the hyperboloid shape are capable of axial movement by adjusting jack bolts connected to one of the hyperboloid halves. One of the halves is limited in axial movement while the other half moves axially away from the restricted half, the movement simultaneously generates the composite pre-load and the metallic riser pre-load. The other version uses fluid pressure between mating faces of the segments to push them apart.

Description

FIELD OF THE INVENTION

This invention relates in general to offshore drilling, and in particular to a method and apparatus for preloading a composite enhanced metallic drilling riser assembly.

BACKGROUND OF THE INVENTION

As floating production platforms are moving to deeper waters, lower weight drilling risers are required. A drilling riser is a large diameter string of pipe made up of sections that are secured together, typically by flanged connections. Metallic drilling and productions risers need to be 30% to 50% lighter than metallic risers used in standard depth platforms. A composite overwrap on a metallic tubular improves the hoop characteristics and allows the riser weight to be reduced by approximately 30%. However, a further reduction to 50% requires a unique method to not only support the hoop loading, but also to carry a larger portion of the axial loading. Problems exist in transferring axial loading from the metallic tubular to the composite in a composite enhanced metallic drilling riser system.

SUMMARY OF THE INVENTION

In view of the foregoing, embodiments of the present invention beneficially provide an offshore composite enhanced metallic drilling riser equipped to enable preloading of the composite shell and the metallic cylinder. The composite enhanced metallic drilling riser system as comprised by the present invention comprises steel end connectors and a continuous metallic cylinder, encased in a composite shell. A segmented hyperboloid shaped profile is located near each of the end fittings for preloading of the composite and the metallic riser. A ring is mounted to the metallic cylinder between the halves of the hyperboloid. Both halves of the hyperboloid shape are capable of axial movement by adjusting jack bolts connected to one of the hyperboloid halves. The other end of the jack bolts are secured to connector flanges on the metallic cylinder. One of the halves is limited in axial movement by the ring surrounding the metallic cylinder. As the other hyperboloid half moves axially away from the restricted half, the movement simultaneously generates the composite pre-load and the metallic cylinder pre-load.

Embodiments of the present invention also provide an alternate embodiment segmented hyperboloid shaped profile located near each of the end fittings for preloading of the composite and the metallic cylinder. In one embodiment, one half of the hyperboloid shape is moved axially to generate the composite pre-load. Pressure is introduced by a radial port between the metallic cylinder and the composite and enters at the vertical plane of the two hyperboloid halves, to drive the two axially apart. A ratcheting thread is located on the horizontal interface between the hyperboloid half and the metallic cylinder, to maintain the axial position of the hyperboloidal profile while pre-loading the composite. An inwardly biased “C-ring” is located at the vertical plane of the two hyperboloids, and moves radially into the axial gap created between the hyperboloid halves. The width of the “C-ring” allows the calculated pre-load to be maintained, prohibiting the hyperboloid halves from moving closer to one another.

In view of the foregoing, the present invention provides an apparatus and method which utilizes the movement of hyperboloid shaped halves in order to provide a reliable method of pre-loading the composite material and the cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a composite enhanced drilling riser assembly constructed in accordance with this invention.

FIG. 2 is a sectional view of the composite enhanced drilling riser assembly ofFIG. 1, during a first portion of a process for preloading the composite enhanced drilling riser assembly.

FIG. 3 is a sectional view of the composite enhanced drilling riser assembly ofFIG. 1, after the process of preloading the composite enhanced drilling riser is completed.

FIG. 4 is a sectional view of the ring attachment taken along the line4-4 ofFIG. 2.

FIG. 5 is a sectional view of the inner tail piece taken along the line5-5 ofFIG. 1.

FIG. 6 is a sectional view of a composite enhanced drilling riser assembly constructed in accordance with an alternate embodiment of this invention.

FIG. 7 is a schematic sectional view of the composite enhanced drilling riser assembly ofFIG. 6 after preloading.

FIG. 8 is an enlarged sectional view of the threaded interface of the composite enhanced drilling riser assembly ofFIGS. 6 and 7.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, a drilling riser assembly, represented generally byreference numeral20, is presented. The drilling riser assembly comprises ametallic cylinder21 made up of sections of riser pipe secured together. In this embodiment, the various pipe sections are secured together byflanges22 and bolts (not shown), but other means are feasible, such as by radially moving dogs.Flange sections22 are welded onto each end ofmetallic cylinders21.

Aring23 is placed around and welded tometallic riser21.Ring23 contains a set ofmilled slots25 in its outboard face (FIG. 4). Two segments,inner tail piece26 andouter tail piece27, form a hyperboloid shaped profile when positioned together aroundmetallic cylinder21.Inner tail piece26 is machined with ashoulder28 on its interior surface, allowing it to pass over and move relative toring23.Tabs29 are securely attached toinner tail piece26 and align withmilled slots25 on ring23 (FIG. 5). Milledslots25 and matchingtabs29 ensure thatinner tail piece26 does not rotate about the axis ofmetallic cylinder21.

Ring23 is captured betweeninner tail piece26 andtabs29. The axial movement ofinner tail piece26 is limited in range byshoulder28 andtabs29.Outer tail piece27 is placed aroundmetallic cylinder21 and positioned in abutment withinner tail piece26 andtabs29, forming a hyperboloid shaped profile. The end ofouter tail piece27closest connector flange22 is machined with a plurality of threadedholes31 capable of receivingjack bolts33.Jack bolts33 extend through apertures onflange22 and screw into threadedholes31 onouter tail piece27. Oncering23,inner tail piece26, andouter tail piece27 are assembled oncylinder21, a mold release agent is placed over these components, ensuring that thecomposite layer37 does not bond to the components during the application process.

Acomposite layer37 is then formed over themetallic riser21,inner tail piece26, andouter tail piece27. The composite fabrication process may be accomplished by a variety of processes including, for example, filament winding, tape laying, roll wrapping, and hand layup. Once the composite has cured, the assembly is ready to be preloaded.

Referring generally toFIGS. 1-3, theriser assembly20 comprises a preloading system that is adapted to apply a tensile load to thecomposite layer37 and apply a compressive load to thecylinder21. Asjack bolts33 are tightened,outer tail piece27 is moved axially towardflange22. Asouter tail piece27 moves closer toflange22, the movement simultaneously causescomposite layer37 to move axially towardflange22. Asouter tail piece27, andcomposite layer37 move,inner tail piece26 also moves closer towardflange22, whilering23 remains fixed tocylinder21. The axial movement of thecomposite layer37 with respect tocylinder21 results in a tension preload incomposite layer37 which is balanced by a compression preload in cylinder21 (FIG. 3), as represented by arrows. The preload of thecomposite37 againstcylinder21 relievescylinder21 of some portion of the externally applied tensile load borne by theriser joint assembly20 when it is placed in service within a riser string. Theriser assembly20 allows the apportionment of the applied load carried between thecylinder21 and thecomposite37 to be controlled and optimized.

Inner tail piece26 is able to move axially towardflange22, but is limited in range byshoulder28 contactingring23. Whenshoulder28 comes into contact withring23,inner tail piece26 can no longer move axially. As illustrated byFIG. 3,jack bolts33 may be turned even further, resulting in increased axial movement ofouter tail piece27, and an increased distance betweeninner tail piece26 andouter tail piece27. The movement forcesinner tail piece26 andouter tail piece27 into greater contact with the inner surfaces oflayer37, increasing pre-loading of the composite to metal joint.

The axial movement ofouter tail piece27 away frominner tail piece26 increases the contact pressure betweentail pieces26,27 andcomposite37. This increased contact pressure creates an internal preload betweenmetallic components26,27 andcomposite37 of the composite to metallic interface. The preload prevents looseness or relative motion betweencomposite37 andcomponents26,27, increasing fatigue performance.

Asouter tail piece27 moves closer to flange22, the movement simultaneously causescomposite layer37 to move, placing the composite structure in increased tension. Ascomposite layer37 is placed in increased tension,metallic cylinder21 is placed in increased compression. The result is simultaneous pre-loading ofcomposite structure37 andmetallic cylinder21. The end ofcylinder21 opposite the end shown may have a similar arrangement to apply tension and enhance bonding ofcomposite layer37.

Referring generally toFIGS. 6-8, an alternate embodiment of a drilling riser is presented. Referring toFIG. 6, theriser assembly41 includes ametallic cylinder43 made up of sections of riser pipe secured together. In this embodiment, the various pipe sections are secured together byflanges45 and bolts (not shown).Flange sections45 are welded onto each end ofmetallic cylinders43. Floatingsegment47 and fixedsegment49 form a hyperboloid shaped profile when positioned together aroundmetallic cylinder43.Segment49 is shaped as half of a hyperboloid, and is fixed tocylinder43;segment49 may be formed integrally as part ofcylinder43.Segment47, the other half of the hyperboloid, is connected to themetallic cylinder43 by way of aratchet interface arrangement51. The twosegments47,49 are positioned in abutment with one another to form a hyperboloid shaped profile near the end segments of eachcylinder43.

Referring toFIG. 8, ratchetinterface51 may include asplit ring53 with external teeth55.Split ring53 is carried in arecess56 ofsegment47.Split ring53 is biased inward into engagement with thread orgrooves57 formed on the exterior ofcylinder43. Teeth55 are saw-toothed in shape. Assegment47 moves in the direction of the arrow,ring53 expands and contracts, with teeth55 moving overgrooves57.

Anangled shoulder59 is located on the outer diameter offace61 ofsegment47.Face61 is perpendicular to the axis ofcylinder43 and initially abuts asimilar face63 onsegment49. An inwardly biased C-ring65, of a predetermined width is held inshoulder59. Anaccess port67 is located radially outwards fromcylinder43, extends axially along the length ofcylinder43, passes throughsegment47, and ends at the abutting faces61,63 of the twohyperboloid halves47,49.

A mold release agent is placed over theriser43,segments47,49, C-ring65, andport67, ensuring that the composite material does not bond to these components during the application process. Acomposite layer71 is then formed over themetallic riser43 and the hyperboloid shaped profile. The composite fabrication process may be accomplished by a variety of processes including, for example, filament winding, tape laying, roll wrapping, and hand layup. Once the composite has cured, the assembly is ready to be preloaded.

As illustrated byFIG. 7, air or another fluid is introduced throughpressure port67, and enters between faces61,63 of the twohyperboloid halves47,49, driving the two axially apart as pressure increases. Ratchetingthread arrangement51 maintains the axial position of thehyperboloidal profile47 while pre-loading the composite71. As pressure is supplied toport67, the pressure build up between faces61,63 ofsegments47,49causes segment47 to move away fromsegment49 and towardflange45. Inwardly biased C-ring65 slides on taperedshoulder59 and moves radially into the axial gap created between thefaces61,63 of hyperboloid halves47,49. The width of C-ring65 allows the calculated pre-load to be maintained, prohibiting the hyperboloid halves47,49 from moving closer to one another. Assegment47 moves axially,composite layer71 is placed in tension. The movement ofsegment47 also causes pre-loading of the composite to metal joint due to the increased contact between thecomposite layer71 andsegments47,49.

Alternatively, the positions ofsegments47,49 could be switched so thatsegment49 move axially away fromflange45. This arrangement would provide a means for pre-loading the composite to metal joint. However, the arrangement would not place the entirecomposite structure71 in tension as the previous arrangement.

While the invention has been shown in only two of its forms, it should be apparent to those skilled in the art that it is not so limited but susceptible to various changes without departing from the scope of the invention.

Claims (20)

1. A composite enhanced metallic drilling pipe comprising:

a hollow cylinder, comprising a metal, having a central longitudinal axis;

a sleeve, comprising a composite material, disposed over at least a portion of the hollow cylinder; and

a preloading mechanism, comprising a first segment and a second segment, the second segment being axially movable relative to the cylinder, wherein the preloading mechanism is adapted to enable the second segment to be moved axially relative to the cylinder to apply a tensile force to the sleeve and a compressive force to the hollow cylinder.

2. The pipe ofclaim 1 wherein each of the segments is mounted on an outer diameter portion of the cylinder.

3. The pipe ofclaim 1 wherein:

the pipe has a flange section extending axially from the cylinder; and

the second segment is connected to the flange section by an adjustable bolt that extends from the flange section to the second segment for axially moving the second segment.

4. The pipe ofclaim 1 wherein the first segment is rigidly connected to the cylinder.

5. The pipe ofclaim 1 wherein the pretension mechanism comprises a ratcheting interface between the second segment and the cylinder so as to allow axial movement of the second segment in one direction, but prevent axial movement in the opposite direction.

6. The pipe ofclaim 1 wherein the second segment is capable of moving axially relative to the first segment from an initial position wherein the pretension mechanism further comprises a spacing member, positioned between the first and second segments while at a desired spacing between each others to maintain said desired spacing.

7. The pipe ofclaim 1 wherein the segments have an exterior contour that is hyperboloidal.

8. The pipe ofclaim 1 wherein each of the segments is capable of axial movement relative to the cylinder, but the second segment is capable of greater axial movement relative to the cylinder than the first segment.

9. The pipe ofclaim 1 wherein the pretension mechanism comprises a fluid conduit to introduce fluid pressure to drive the second segment apart from the first segment.

10. A composite enhanced metallic pipe comprising:

a hollow metallic cylinder extending along a central longitudinal axis;

first and second segments disposed around the cylinder and defining a selected contour, the segments being axially moveable relative to the cylinder;

a sleeve of composite material formed about the cylinder and over the contour of the segments;

a flange section extending axially from an end of the cylinder, the second segment being closer to the flange than the first segment;

a restrictive member, securely joined to the cylinder between the first and second segments for limiting the axial movement of the first segment to a selected distance; and

an adjustable link extending from the second segment to the flange such that adjustment of the link moves the second segment axially, applying tension to the sleeve and bringing along with it the first segment until the first segment contacts the restrictive member, wherein continued adjustment of the link causes the second segment to move axially apart from the first segment.

11. The pipe ofclaim 10 wherein the contour is hyperboloidal.

12. The pipe ofclaim 10 further comprising anti-rotation tabs (29) located on the first segment for engagement with anti-rotation slots (25) on the restrictive member, restricting the rotation of the first segment about the cylinder.

13. A composite enhanced metallic pipe comprising:

a hollow metallic cylinder extending along a central longitudinal axis;

first and second segments disposed around the cylinder and defining a selected contour, the first segment rigidly connected to the cylinder, the second segment capable of axial movement, wherein the segments have mating faces in an initial position; and

a fluid passage to deliver fluid pressure and force to move the second segment axially away from the first segment.

14. The pipe ofclaim 13 further comprising an inwardly biased split ring carried in a recess in one of the faces that moves between the faces to hold apart the first and second segments.

15. A method for preloading a composite enhanced metallic pipe comprising:

forming an axially moveable connection assembly with first and second juxtaposed segments on an end portion of a metallic cylinder;

connecting a flange section to the end of the cylinder;

forming a composite sleeve over the cylinder and the juxtaposed segments; and

moving the second segment axially toward the flange section relative to the cylinder, applying tension to the sleeve and compression to the metallic cylinder.

16. The method ofclaim 15 further comprising:

moving the first segment with the second segment toward the flange section for a limited distance; then

continuing to move the second segment toward the flange section while the first segment remains stationary relative to the cylinder.

17. The method ofclaim 15 wherein moving the second segment comprises attaching the second segment to the flange with a threaded link and adjusting the link.

18. The method ofclaim 15 wherein the first segment is fixed to the cylinder and moving the second segment comprises:

applying fluid pressure between mating faces of the segments.

19. The method ofclaim 15 further comprising connecting a ratchet interface between the second segment and the cylinder that allows movement of the second segment toward the flange, but not away.

20. The method ofclaim 15 further comprising placing a spacer between the mating faces at the desired tension.

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